The invention relates to a timing device for controlling machine tools, handling equipment or other servomechanical devices, and to a method of manufacture. The timing device typically comprises a timing control element, a transmitter, and a receiver.
In general, timing control elements are either rotatable about a central axis, i.e., timing disk, or are movable in a linear direction, i.e., timing rule. Light, projected by a transmitter, passes through the control element, and is intercepted by the receiver. The receiver, responsive to the light, converts the light into an electrical signal capable of controlling machinery and other servomechanical devices.
Timing control elements typically are encoded with a selected window pattern, i.e., they have an annular or linear array of windows which alternate in a transparent window, opaque window, transparent window, opaque window pattern. While the transparent window openings allow the transmitted light to pass through the timing disk or rule, the opaque windows prevent the light from passing through the timing disk or rule.
Timing disks as a rule are fixed to a rotating shaft by means of a hub. For linear systems, timing rules are arranged at right angles to a source of light and the associated receiver generates an electrical signal in response to the incoming light. This particular application is used, for example, to control the feeding action of machine tools.
As the timing disk rotates or the timing rule moves in a linear direction, light is directed at the selected window pattern. Because of the window pattern, the transmitted light can only pass through a transparent window. In response to the light, the receiver generates an electrical signal.
The electrical signals serve to establish a control surface for the measurement of rotational speed, acceleration and more accurate positioning of servomechanical elements, as for example a printing head, a robot arm or a tool carrier.
Timing control elements can be made of glass, metal or plastic, however, plastic and metal are typically used in mass production applications. They are produced, for example, in the case of angle indicators or encoding units, e.g. ink jet printers, out of transparent films.
Timing control elements are generally constructed of light-sensitive film. Coding of the film occurs when the film is exposed to light passed through a template means. The coding results in the production of an alternating pattern of transparent and opaque windows. Individual disks or rules are then cut out of the film material to generate timing disks or timing rules, respectively.
Known timing devices utilize an arrangement whereby the transmitter is placed on one side of the timing structure and the receiver is placed on the other side of the timing structure to capture the light as it passes through the disk. This arrangement has been known to cause a number of problems, including: a requirement for a complex electro-mechanical apparatus, increased mechanical stress caused by oscillating loads, a larger footprint size for the timing device, and dirt forming on the timing structure, thereby preventing light from passing efficiently through the structure.